Angela Merkel and Francois Hollande will press Vladimir Putin for a cease-fire in Ukraine on Friday as U.S. and Russian officials expressed skepticism that a quick resolution to stem the spiraling violence is possible.

After meeting Ukrainian President Petro Poroshenko on Thursday, the German and French leaders head to Moscow on Friday to present an alternative to a peace proposal drawn up by Putin that laid separatist claim to swathes of eastern Ukrainian territory. The U.S is also working to "change Russia's behavior," said Secretary of State John Kerry, who also met Poroshenko in Kiev, though President Barack Obama's administration said a deal may be tough to achieve.

"We have seen the Ukrainian government live up to a lot of those agreements and at least try to implement them," White House Press Secretary Josh Earnest said Thursday. "But those efforts have been entirely undermined by Russian-backed separatists with the full support of Russia completely ignoring those commitments."